Heart Anatomy and Pericardium Overview

Heart Anatomy

• The heart is about the size of a fist.
• It's located superior to the diaphragm, left of the midline, anterior to the vertebral column, and posterior to the sternum.

Coverings of the Heart

• The pericardium is a double-walled sac that surrounds the heart.
• The fibrous pericardium is the superficial layer.
• The serous pericardium is the deep layer, which is further divided into the parietal layer (lining the fibrous pericardium) and the visceral layer (lining the heart surface).
• The pericardial cavity is the space between the parietal and visceral layers and contains fluid.

Function of the Pericardium

• Protects and anchors the heart.
• Prevents overfilling of the heart with blood.
• Allows the heart to function in a friction-free environment.

Heart Wall

• Epicardium: The visceral layer of the serous pericardium.
• Myocardium: The cardiac muscle layer, making up the bulk of the heart.
• Fibrous skeleton: A crisscrossing, interlacing layer of connective tissue.
• Endocardium: The endothelial layer lining the inner myocardial surface.

External Heart: Major Vessels

• Vessels returning blood to the heart:
  • Superior and inferior venae cavae
  • Right and left pulmonary veins
• Vessels conveying blood away from the heart:
  • Pulmonary trunk (splits into right and left pulmonary arteries)
  • Ascending aorta (three branches):
    • Brachiocephalic artery
    • Left common carotid artery
    • Subclavian arteries

External Heart: Vessels that Supply/Drain the Heart

• Arteries:
  • Right and left coronary arteries (in atrioventricular groove)
  • Marginal artery, circumflex artery, and anterior interventricular artery
• Veins:
  • Small cardiac vein, anterior cardiac vein, and great cardiac vein

Atria

• Receiving chambers of the heart.
• Each atrium has a protruding auricle.
• Pectinate muscles mark atrial walls.
• Right atrium receives blood from the superior and inferior venae cavae and coronary sinus.
• Left atrium receives blood from pulmonary veins.

Ventricles

• Discharging chambers of the heart.
• Papillary muscles and trabeculae carneae muscles mark ventricular walls.
• Right ventricle pumps blood into the pulmonary trunk.
• Left ventricle pumps blood into the aorta.

Myocardial Thickness

• Atria have thin walls and deliver blood to adjacent ventricles.
• Ventricle walls are thicker and stronger.
• The right ventricle wall is thicker than the left because it pumps blood to the lungs (low flow resistance).
• The left ventricle wall is the thickest because it pumps blood to the systemic circulation.

Pathway of Blood Through the Heart and Lungs

• Right atrium -> tricuspid valve -> right ventricle -> pulmonary semilunar valve -> pulmonary arteries -> lungs -> pulmonary veins -> left atrium -> bicuspid valve -> left ventricle -> aortic semilunar valve -> aorta -> systemic circulation

Coronary Circulation

• The functional blood supply to the heart muscle.
• Collateral routes ensure blood delivery to the heart even if major vessels are blocked.

Heart Valves

• Ensure unidirectional blood flow through the heart.
• Atrioventricular (AV) valves:
  • Lie between the atria and ventricles.
  • Prevent backflow into the atria when ventricles contract.
  • Anchored to papillary muscles by chordae tendineae.
• Semilunar valves:
  • Prevent backflow of blood into the ventricles.
  • Aortic semilunar valve: between left ventricle and aorta.
  • Pulmonary semilunar valve: between right ventricle and pulmonary trunk.

Microscopic Anatomy of Heart Muscle

• Cardiac muscle is striated, short, fat, branched, and interconnected.
• Connective tissue endomysium acts as both tendon and insertion.
• Intercalated discs anchor cardiac cells and allow free passage of ions.
• Heart muscle behaves as a functional syncytium.

Explore the fascinating structure of the heart, including its size, location, and coverings. This quiz examines the pericardium's role in protecting and anchoring the heart as well as the distinct layers of the heart wall. Test your knowledge on these essential aspects of heart anatomy.